Scientific Thinking Handbook R2
Making Observations R2
Predicting and Hypothesizing R3
Identifying Cause and Effect R5
Recognizing Bias R6
Identifying Faulty Reasoning R7
Analyzing Statements R8
Lab Handbook R10
Safety Rules R10
Using Lab Equipment R12
The Metric System and SI Units R20
Precision and Accuracy R22
Making Data Tables and Graphs R23
Designing an Experiment R28
Math Handbook R36
Describing a Set of Data R36
Using Ratios, Rates, and Proportions R38
Using Decimals, Fractions, and Percents R39
Using Formulas R42
Finding Areas R43
Finding Volumes R43
Using Significant Figures R44
Using Scientific Notation R44
Note-Taking Handbook R45
Note-Taking Strategies R45
Vocabulary Strategies R50
An observation is an act of noting and recording an event, characteristic, behavior, or anything else detected with an instrument or with the senses.
Observations allow you to make informed hypotheses and to gather data for experiments. Careful observations often lead to ideas for new experiments. There are two categories of observations:
Quantitative observations can be expressed in numbers and include records of time, temperature, mass, distance, and volume.
Qualitative observations include descriptions of sights, sounds, smells, and textures.
A student dissolved 30 grams of Epsom salts in water, poured the solution into a dish, and let the dish sit out uncovered overnight. The next day, she made the following observations of the Epsom salt crystals that grew in the dish.
Table 1. Observations of Epsom Salt Crystals
To determine the mass, the student found the mass of the dish before and after growing the crystals and then used subtraction to find the difference.
The student measured several crystals and calculated the mean length. (To learn how to calculate the mean of a data set, see page R36.)
mean crystal length = 0.5 cm
longest crystal length = 2 cm
Crystals are clear.
Crystals are long, thin, and rectangular.
White crust has formed around edge of dish. Photographs or sketches are useful for recording qualitative observations.
Epsom salt crystals
MORE ABOUT OBSERVING
Make quantitative observations whenever possible. That way, others will know exactly what you observed and be able to compare their results with yours.
It is always a good idea to make qualitative observations too. You never know when you might observe something unexpected.
Predicting and Hypothesizing
A prediction is an expectation of what will be observed or what will happen. A hypothesis is a tentative explanation for an observation or scientific problem that can be tested by further investigation.
Suppose you have made two paper airplanes and you wonder why one of them tends to glide farther than the other one.
1. Start by asking a question.
2. Make an educated guess. After examination, you notice that the wings of the airplane that flies farther are slightly larger than the wings of the other airplane.
To read about independent and dependent variables, see page R30.
3. Write a prediction based upon your educated guess, in the form of an “If…, then…?? statement. Write the independent variable after the word if, and the dependent variable after the word then.
4. To make a hypothesis, explain why you think what you predicted will occur. Write the explanation after the word because.
1. Why does one of the paper airplanes glide farther than the other?
2. The size of an airplane's wings may affect how far the airplane will glide.
3. Prediction: If I make a paper airplane with larger wings, then the airplane will glide farther.
Notice that the part of the hypothesis after because adds an explanation of why the airplane will glide farther.
4. Hypothesis: If I make a paper airplane with larger wings, then the airplane will glide farther, because the additional surface area of the wing will produce more lift.
MORE ABOUT HYPOTHESES
The results of an experiment cannot prove that a hypothesis is correct. Rather, the results either support or do not support the hypothesis.
Valuable information is gained even when your hypothesis is not supported by your results. For example, it would be an important discovery to find that wing size is not related to how far an airplane glides.
In science, a hypothesis is supported only after many scientists have conducted many experiments and produced consistent results.
An inference is a logical conclusion drawn from the available evidence and prior knowledge. Inferences are often made from observations.
A student observing a set of acorns noticed something unexpected about one of them. He noticed a white, soft-bodied insect eating its way out of the acorn.
The student recorded these observations.
There is a hole in the acorn, about 0.5 cm in diameter, where the insect crawled out.
There is a second hole, which is about the size of a pinhole, on the other side of the acorn.
The inside of the acorn is hollow.
Here are some inferences that can be made on the basis of the observations.
The insect formed from the material inside the acorn, grew to its present size, and ate its way out of the acorn.
The insect crawled through the smaller hole, ate the inside of the acorn, grew to its present size, and ate its way out of the acorn.
An egg was laid in the acorn through the smaller hole. The egg hatched into a larva that ate the inside of the acorn, grew to its present size, and ate its way out of the acorn.
When you make inferences, be sure to look at all of the evidence available and combine it with what you already know.
MORE ABOUT INFERENCES
Inferences depend both on observations and on the knowledge of the people making the inferences. Ancient people who did not know that organisms are produced only by similar organisms might have made an inference like the first one. A student today might look at the same observations and make the second inference. A third student might have knowledge about this particular insect and know that it is never small enough to fit through the smaller hole, leading her to the third inference.